<title> [Usaco2005 nov]Asteroids 穿越小行星群</title><link href="http://hzoi.com/tomorrow.css" rel="stylesheet"><div class="ui existing segment"><pre><code><span class="pl-cp">#include</span> <span class="pl-cpf">&lt;algorithm&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#include</span> <span class="pl-cpf">&lt;cstdio&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#include</span> <span class="pl-cpf">&lt;cstring&gt;</span><span class="pl-cp"></span>
<span class="pl-k">using</span> <span class="pl-k">namespace</span> <span class="pl-n">std</span><span class="pl-p">;</span>
<span class="pl-k">const</span> <span class="pl-kt">double</span> <span class="pl-n">eps</span> <span class="pl-o">=</span> <span class="pl-mf">1e-9</span><span class="pl-p">;</span>
<span class="pl-kt">int</span> <span class="pl-n">head</span><span class="pl-p">[</span><span class="pl-mi">505</span><span class="pl-p">],</span> <span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-mi">10005</span><span class="pl-p">],</span> <span class="pl-n">nxt</span><span class="pl-p">[</span><span class="pl-mi">10005</span><span class="pl-p">],</span> <span class="pl-n">tot</span><span class="pl-p">,</span> <span class="pl-n">n</span><span class="pl-p">,</span> <span class="pl-n">k</span><span class="pl-p">,</span> <span class="pl-n">link</span><span class="pl-p">[</span><span class="pl-mi">505</span><span class="pl-p">],</span> <span class="pl-n">ans</span><span class="pl-p">;;</span>
<span class="pl-kr">inline</span> <span class="pl-kt">void</span> <span class="pl-nf">add</span><span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">x</span><span class="pl-p">,</span> <span class="pl-kt">int</span> <span class="pl-n">y</span><span class="pl-p">)</span> <span class="pl-p">{</span>
    <span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-o">++</span><span class="pl-n">tot</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">y</span><span class="pl-p">,</span> <span class="pl-n">nxt</span><span class="pl-p">[</span><span class="pl-n">tot</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">head</span><span class="pl-p">[</span><span class="pl-n">x</span><span class="pl-p">],</span> <span class="pl-n">head</span><span class="pl-p">[</span><span class="pl-n">x</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">tot</span><span class="pl-p">;</span>
<span class="pl-p">}</span>
<span class="pl-kt">bool</span> <span class="pl-n">cover</span><span class="pl-p">[</span><span class="pl-mi">505</span><span class="pl-p">];</span>
<span class="pl-kt">bool</span> <span class="pl-nf">find</span><span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">k</span><span class="pl-p">)</span> <span class="pl-p">{</span>
    <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-n">head</span><span class="pl-p">[</span><span class="pl-n">k</span><span class="pl-p">];</span> <span class="pl-n">i</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-n">nxt</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">])</span> <span class="pl-p">{</span>
        <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-o">!</span><span class="pl-n">cover</span><span class="pl-p">[</span><span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">]])</span> <span class="pl-p">{</span>
            <span class="pl-kt">int</span> <span class="pl-n">q</span> <span class="pl-o">=</span> <span class="pl-n">link</span><span class="pl-p">[</span><span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">]];</span>
            <span class="pl-n">link</span><span class="pl-p">[</span><span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-n">k</span><span class="pl-p">;</span>
            <span class="pl-n">cover</span><span class="pl-p">[</span><span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span>
            <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">q</span> <span class="pl-o">==</span> <span class="pl-o">-</span><span class="pl-mi">1</span><span class="pl-p">)</span> <span class="pl-p">{</span>
                <span class="pl-n">ans</span><span class="pl-o">++</span><span class="pl-p">;</span>
                <span class="pl-k">return</span> <span class="pl-nb">true</span><span class="pl-p">;</span>
            <span class="pl-p">}</span>
            <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">find</span><span class="pl-p">(</span><span class="pl-n">q</span><span class="pl-p">))</span> <span class="pl-k">return</span> <span class="pl-nb">true</span><span class="pl-p">;</span>
            <span class="pl-n">link</span><span class="pl-p">[</span><span class="pl-n">to</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">]]</span> <span class="pl-o">=</span> <span class="pl-n">q</span><span class="pl-p">;</span>
        <span class="pl-p">}</span>
    <span class="pl-p">}</span>
    <span class="pl-k">return</span> <span class="pl-nb">false</span><span class="pl-p">;</span>
<span class="pl-p">}</span>
<span class="pl-kt">int</span> <span class="pl-nf">main</span><span class="pl-p">()</span> <span class="pl-p">{</span>
    <span class="pl-n">scanf</span><span class="pl-p">(</span><span class="pl-s">&quot;%d%d&quot;</span><span class="pl-p">,</span> <span class="pl-o">&amp;</span><span class="pl-n">n</span><span class="pl-p">,</span> <span class="pl-o">&amp;</span><span class="pl-n">k</span><span class="pl-p">);</span>
    <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-mi">0</span><span class="pl-p">,</span> <span class="pl-n">x</span><span class="pl-p">,</span> <span class="pl-n">y</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">&lt;</span> <span class="pl-n">k</span><span class="pl-p">;</span> <span class="pl-n">i</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
        <span class="pl-n">scanf</span><span class="pl-p">(</span><span class="pl-s">&quot;%d%d&quot;</span><span class="pl-p">,</span> <span class="pl-o">&amp;</span><span class="pl-n">x</span><span class="pl-p">,</span> <span class="pl-o">&amp;</span><span class="pl-n">y</span><span class="pl-p">);</span>
        <span class="pl-n">add</span><span class="pl-p">(</span><span class="pl-n">x</span><span class="pl-p">,</span> <span class="pl-n">y</span><span class="pl-p">);</span>
    <span class="pl-p">}</span>
    <span class="pl-n">memset</span><span class="pl-p">(</span><span class="pl-n">link</span><span class="pl-p">,</span> <span class="pl-o">-</span><span class="pl-mi">1</span><span class="pl-p">,</span> <span class="pl-k">sizeof</span> <span class="pl-n">link</span><span class="pl-p">);</span>
    <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">&lt;=</span> <span class="pl-n">n</span><span class="pl-p">;</span> <span class="pl-n">i</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
        <span class="pl-n">memset</span><span class="pl-p">(</span><span class="pl-n">cover</span><span class="pl-p">,</span> <span class="pl-mi">0</span><span class="pl-p">,</span> <span class="pl-k">sizeof</span> <span class="pl-n">cover</span><span class="pl-p">);</span>
        <span class="pl-n">find</span><span class="pl-p">(</span><span class="pl-n">i</span><span class="pl-p">);</span>
    <span class="pl-p">}</span>
    <span class="pl-n">printf</span><span class="pl-p">(</span><span class="pl-s">&quot;%d</span><span class="pl-se">\n</span><span class="pl-s">&quot;</span><span class="pl-p">,</span> <span class="pl-n">ans</span><span class="pl-p">);</span>
    <span class="pl-k">return</span> <span class="pl-mi">0</span><span class="pl-p">;</span>
<span class="pl-p">}</span>
</cpde></pre></div>